Fluid streams comprising small constituents are produced by many chemical and combustion processes, such as, but not limited to, particulates in the exhaust gas stream of coal fired power plants. Such particulate matter is undesirable and should be removed before the gas stream is passed to equipment or processes and released into the atmosphere. It is particularly challenging to remove such particulate matter from high temperature gas streams in large volumes exhausted from boilers of such power generating facilities.
Particles which are over ten microns in diameter are frequently removed from gas streams by conventional porous filters, such as bag houses and the like, but smaller particles are much more difficult to remove because the porosity of the filter must be so small to capture these fine particles that it creates a substantial pressure drop across the filter. The pressure drop is problematic, consumes energy resources and may inhibit the combustion process. Therefore, porous filters cannot remove small particles from gas streams efficiently.
From time to time, particulates in a gas stream collide with one another and may naturally agglomerate with other such particles on impact to form larger agglomerated particles. This agglomeration is beneficial because the agglomerated particles are larger and thus susceptible to filtration from the porous filters. However, such incidences of natural agglomeration are limited. Increasing the incidence of collisions and agglomeration results in a reduced emission of such particulates into the atmosphere. For this reason, many methods of agglomerating these particles have been employed. The number of collisions may be increased by confining the gas stream in a tube, flue, or duct and subjecting the particles to a sonic or acoustic field. This process is referred to as acoustic agglomeration and has been employed to agglomerate small particles into larger agglomerates.
However, methods of acoustic agglomeration are frequently inefficient in that the power consumption required by such devices negates the benefits achieved by only marginal reduction in the particulates exhausted into the atmosphere. Methods of acoustically agglomerating particulates employing a sound source emitting a fixed or constant frequency or employing a pulse combustor producing a saw-tooth wave have been employed.
Such systems, however, suffer from deficiencies including lacking sufficient control of the particulate agglomeration, failing to agglomerate particulates of a small size, and inefficiency in agglomeration and power consumption when compared to the actual reduction in particulate emission.
Thus, a need exists for an improved system and method for acoustically agglomerating constituents in a fluid stream. Furthermore, a need exists for a more efficient system and method for acoustically agglomerating particulates in the fluid stream capable of achieving consistent and controlled constituent agglomeration. It is to such an acoustic agglomeration system and method that the present invention is directed.